Francisco de Assis Pujol Goulart

Background: Hairy beggarticks (Bidens pilosa L.) is a highly adaptable weed species that thrives in diverse environmental conditions. Understanding the environmental factors that influence its germination is essential for developing predictive emergence models and supporting integrated management strategies. Objective: The present study aimed to estimate the cardinal temperatures and water potentials for B. pilosa germination, assess seed bank longevity, and develop a field-based emergence model. Methods: Laboratory experiments were conducted to determine base temperature and water potential thresholds for [...] Abstract Background: Hairy beggarticks (Bidens pilosa L.) is a highly adaptable weed species that thrives in diverse environmental conditions. Understanding the environmental factors that influence its germination is essential for developing predictive emergence models and supporting integrated management strategies. Objective: The present study aimed to estimate the cardinal temperatures and water potentials for B. pilosa germination, assess seed bank longevity, and develop a field-based emergence model. Methods: Laboratory experiments were conducted to determine base temperature and water potential thresholds for

Background Weed competition is one of the main constraints to rice yield. Objective Determine the period prior to interference (PPI) of barnyardgrass ( Echinochloa spp.) on the irrigated rice crop as a function of the application of the herbicide cyhalofop-butyl alone and associated with penoxsulam. Methods A field experiment was carried out in a randomized block design, with four replications. The treatments were arranged in a 2×7 factorial scheme, with factor A consisting of the herbicides cyhalofop-butyl and the [...] Abstract Background Weed competition is one of the main constraints to rice yield. Objective Determine the period prior to interference (PPI) of barnyardgrass ( Echinochloa spp.) on the irrigated rice crop as a function of the application of the herbicide cyhalofop-butyl alone and associated with penoxsulam. Methods A field experiment was carried out in a randomized block design, with four replications. The treatments were arranged in a 2×7 factorial scheme, with factor A consisting of the herbicides cyhalofop-butyl and the

Background: Weedy rice belongs to the same taxon as irrigated rice (Oryza sativa L.), and is the main weed of the crop. However, it exhibits different traits that produce greater competitive capacity using solar radiation. In competition for light, plants invest in photoassimilates for the shoots and can reduce their root development. Objectives: The objective of this work is to evaluate the initial growth of weedy and cultivated rice roots in response to light competition. Methods: The experiment was conducted in a greenhouse (hydroponic system), using a completely randomized design, arranged in a 2x2x6 factorial scheme, with five replications. Factor A consisted of the weedy rice biotype Q35B and the rice cultivar IRGA 424; factor B of light competition conditions (presence or absence of 75 weedy rice plants); and factor C of assessment time. At 0, 7, 14, 21, 28 and 35 days after transplanting, samples were taken from each experimental unity to measure the root area, perimeter, length, number of tips, and root dry weight (RDW), and shoot dry weight (SDW). Results: Competition for light reduced the area, perimeter, length, number of root tips, reduced the RDW and the SDW of both, the weedy rice biotype and crop rice. However, regardless of the competitive condition, the weedy rice showed a higher area, perimeter, initial growth, number of tips, RDW and SDW than that of cultivated rice. Conclusion: Weedy rice exhibits greater competitive capacity using the resources beneath the soil.

Biochemical assays in a time-course were employed to evaluate stresses induced by glyphosate treatment in resistant and sensitive biotypes of Conyza bonariensis. Two experiments were conducted assessing glyphosate doses and time-course after treatment. The doses of glyphosate ranged from 0 to 11840 g ae·ha^–1 and assessments performed until 552 h after glyphosate treatment (HAT). The objectives of this study were to evaluate the oxidative stress and differential antioxidant enzyme activity in glyphosate-resistant and -sensitive biotypes of hairy fleabane after glyphosate treatment. After treatment, both studied biotypes accumulated similar levels of shikimic-acid until 96 h. The sensitive biotype died at192 HAT. Shikimic-acid and hydrogen peroxide (H₂O₂) accumulation in glyphosate-resistant biotype were transient and did not differ from untreated plants at 288 and 500 HAT, respectively. In both glyphosate-resistant and -sensitive biotypes, a correlation analysis established a cause-and-effect relationship after glyphosate treatment, which leads to shikimic-acid and hydrogen peroxide accumulation, lipid peroxidation (indicates tissue damage) and an enhancement in the activity of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) enzyme. However, in the glyphosate-resistant biotype, the oxidative stress and tissue damage were lower, and antioxidant enzyme activities SOD, CAT, and APX were higher than in the -sensitive biotype. It indicates that antioxidant enzyme in glyphosate-resistant biotype might be related to the glyphosate-resistance process in Conyza bonariensis. This study is the first report of differential antioxidant enzyme activity in hairy fleabane.